When your quarantine is in the same room (and even in a different room) there is always the possibility of spreading something. Mites can travel long distances (hitchhike) and I would assume (maybe someone can back me up on this) that some internal parasites could do the same . I would keep an eye on all of them and use the strictest cleaning regimen and care possible. It seems like it might be overkill to spend that kind of money to treat everyone not even knowing if they are infected.